Locks which provide security on one side and easy and quick operation from the other side are used widely, particularly for doors providing an emergency exit from a building.
Commonly such locks use an engineered rack and pinion operating mechanism to operate several strong bolts simultaneously to secure the door. The door is thus secured at various points around its perimeter to provide security and prevent access from one side of the door. When such a door is an emergency exit it is necessary to comply with safety requirements to provide an operating lever inside which will operate by a single simple movement to retract the bolts and unlock the door to allow a safe and quick exit through the door from the building. Typically, a horizontal bar is provided on such doors for the operation of the lock mechanism.
Thus for lock mechanisms used for such doors there are conflicting requirements. One requirement is the security to prevent access from one side whilst the other requirement is a safety requirement to provide for simple and quick operation of the lock mechanism from the inside to allow the door to be unlocked quickly in an emergency.
The lock mechanisms currently available with a direct drive mechanism to the bolts such as a rack and pinion do not provide adequate security since they do not provide resistance to the application of pressure to the ends of the bolts.
GB-A-2289084 disclose a lock mechanism for use on a door hinged in a door frame at a first side. The lock mechanism comprises bolt members moveable between an engaged position in the door frame and a disengaged position. The bolt members are arranged to engage said door frame from at least two of the sides of said door which are not hinged. Latch means are arranged to prevent movement of at least one of the bolt members from the engaged position to the disengaged position. A latch release arrangement is used to disengage the latch means and allow movement of the bolt member. The latch release arrangement and the bolt members are arranged to be operable in response to a single movement of an operating member to allow the latch means to be disengaged and the bolt members to be disengaged from said engaged position. The bolt members are arranged to be directly driven between said engaged and disengaged positions by movement of the operating member.
The lock mechanism of GB-A-2289084 utilises a direct drive mechanism between the operating member, e.g. a handle, and the bolt members providing for positive and visible locking since the position of the operating member will indicate whether the bolt members are properly engaged or not. Such a direct driven bolting arrangement provides for a heavy duty lock mechanism which together with the latching arrangement, which operates when the bolt members are engaged, provides for high security.
Typically, such lock mechanisms include three bolt members--a horizontal bolt member, an upper bolt member and a lower bolt member. A European Standard has made the requirement that application of pressure to the end of the lower bolt member which is able to move the lower bolt member from the engaged position to the disengaged position should not be able to effect movement of the remaining bolt members from the engaged position to the disengaged position.
The present invention therefore seeks to provide a lock mechanism which complies with the European Standard.